Abrasive substances have been included in conventional dentifrice compositions in order to remove various deposits, including pellicle film, from the surfaces of teeth. Pellicle film is tightly adherent and often contains brown or yellow pigments that impart an unsightly appearance to the teeth. While cleaning is important, the abrasive should not be so aggressive so as to damage the teeth. Ideally, an effective dentifrice abrasive material maximizes pellicle film removal while causing minimal abrasion and damage to the hard tooth tissues.
In the past, the polishing paste used by a dentist or hygienist was packaged in a jar and the prophy cup attached to a dental hand piece was dipped into the jar and then the prophy cup was applied to the teeth. With the advent of potentially fatal diseases that may be present in an oral cavity, the use of a common jar as a source of polishing material for multiple patients was no longer medically acceptable. To avoid this potential medical problem, the polishing compound was packaged in small sealed containers with enough polishing compound to polish the teeth of a single patient. After a one-time use, such a container was disposed of as waste to prevent the spread of disease to other patients. However, such waste is not ideal.
Paste formulations that are stable could potentially meet a number of requirements, including the ability to be transferred out of a container (such as a tube) via pressure (i.e., squeezing of the tube) as a dimensionally stable paste and to return to its previous state upon removal of such pressure, the ability to be transferred in such a manner to an applicator easily and without flow out of the tube during and after such transference, the propensity to remain dimensionally stable on the applicator prior to use, a reduction of spattering, and the proper feel of the paste in the mouth, at least, for the benefit of the user.
A number of water-insoluble, abrasive polishing agents have been used or described for dentifrice compositions. These abrasive polishing agents include natural and synthetic abrasive particulate materials. The generally known synthetic abrasive polishing agents include amorphous precipitated silicas and silica gels and precipitated calcium carbonate (PCC). Other abrasive polishing agents for dentifrices have included chalk, magnesium carbonate, dicalcium phosphate and its dihydrate forms, calcium pyrophosphate, zirconium silicate, potassium metaphosphate, magnesium orthophosphate, tricalcium phosphate, perlite, and the like.
Conventional processing of perlite consists of comminution of the ore (crushing and grinding), screening, thermal expansion, milling, and air size separation of the expanded material to meet the specification of the finished product. For example, perlite ore is crushed, ground, and separated to a predetermined particle size range (e.g., passing 30 mesh), then the separated material is heated in air at a temperature of 870°-1100° C. in an expansion furnace, where the simultaneous softening of the glass and vaporization of contained water leads to rapid expansion of glass particles to form a frothy glass material with a bulk volume up to 20 times that of the unexpanded ore. The expanded perlite is then air separated to meet the size specification of the final product. The expanded perlite product may further be milled and separated for use as filter aid or filler material.
Perlite-containing pastes have not been capable of being packaged in tubes because the paste is too viscous and dry and thus, cannot be dosed from the tube with a reasonable applied pressure. Therefore, a perlite-containing paste composition that is capable of being dosed from a tube is needed.